A drum can have a drumhead on one or both ends of the drum. The drumhead includes a membrane, typically stretched over a round rim. The drumhead is struck by sticks or hands or some other object that causes the drumhead to vibrate and causes sound to resonate through the drum.
The drumhead fits into a drum hoop (also called a “rim”) that holds the drumhead against a drum shell. Typically, the drum hoop holds the drumhead against the drum shell by bolts (called “tension rods” or “tension bolts”) that go through openings on a flanged rim on the drum hoop and are threaded into lugs attached to the drum shell. In some drums, the drum hoop has a single flange rim with claws or hooks through which the bolts go. When the bolts are tightened, the claws tighten to grab, pull, and hold the drumhead against the drum shell.
The most common type of drum hoop is flanged. Typically, a flanged drum hoop is comprised of metal of varying thickness folded in a series of 90-degree bends. Usually, flanged drum hoops have three bends and are referred to as “triple-flanged” hoops. The metal is usually stamped to bend it. Holes to receive the tension rods are typically punched into the metal.
As with other instruments, a drum must be tuned before use. Typically, a drum hoop has a slightly larger diameter than the drumhead so there is excess space between the drumhead and the drum hoop. A drumhead must be centered in the drum hoop in order for the drum to emit its proper sound. If the drumhead is not centered in the hoop, then the drumhead will not be centered over the drum shell. When this happens, the drumhead can be muffled, and the drum will be improperly tuned and produce poor sound quality.
When tuning a drum, the drumhead must be centered in the drum hoop before tightening the tension bolts. Currently, drums are tuned by visually placing the drumhead in the center of the hoop and gradually tightening the tension bolts one at a time while repeatedly tapping the drumhead to check for proper sound quality and repeatedly visually inspecting the drumhead to ensure that it is centered in the drum hoop. Such repetition causes the drum-tuning process to be tedious and prone to error.